Mixtures of natural rubber latex and aqueous dispersions of reclaimed rubber



Patented June" 16, 1936 UNITED STATES PATENT OFFICE MIXTURES OF NATURALRUBBER LATEX AND AQUEOUS DISPERSIONS 01' RI- CLAIMED RUBBER Jew NoDrawing. Application February 16, 1934, Serial No. 711,556

0 Claims. (01. 134-17) This invention relates to mixtures of naturalrubber latex and aqueous dispersions of reclaimed rubber, moreparticularly aqueous dispersions of reclaimed rubber which have beenmade with soap as the hydrophilic colloid.

Naturally occurring rubber latex and certain types of aqueousdispersions of reclaimed rubber have been mixed with indifferent successin the past by conditioning either or both with dispersingor stabilizingcolloidal materials before admixing in order to prevent subsequentincipient coagulation or gellation of the dispersed rubber particles.Aqueous soap dispersions of reclaimed rubber, by which is meantartificial aqueous dispersions of reclaimed rubber made with soap as thehydrophilic colloid or dispersing agent, have given the most diiilcultyin mixing with natural latex.

The present invention relates to stable compositions containing naturallatex and aqueous soap dispersions of reclaimed rubber prepared in sucha manner that they will not coagulate or gel on standing even afterconsiderable periods of time.

According to the present invention, the aqueous soap dispersion ofreclaimed rubber which is to be admixed with natural latex is soprepared that it has approximately the same osmotic pressure as thenatural latex, and under such conditions the natural latex and thedispersion of reclaimed rubber may be admixed without subsequentcoagulation or gellation. The aqueous soap dispersions of reclaimedrubber are prepared by dispersing reclaimed rubber, such as an alkalireclaim which has been digested or devulcanized in the presence ofsodium hydroxide or potassium hydroxide and the usual plasticizingagents, in water by milling into the reclaim the desired soap as adispersing agent and grad- .ially adding water to the reclaim and soapmixture until a change of phase takes place and the rubber changes fromthe continuous phase into adispersed phase in the aqueous medium. Themethod of preparing such aqueous dispersions of reclaimed rubber arewell known'in the art and are described in detail in the Pratt U. S.Patent 1,732,027 and in other Pratt patents such as 1,755,891,1,755,892, 1,731,725, and 1,762,194. Ii. desired, in lieu of utilizing apreviously prepared soap as the dispersing agent the soap may be formedin situ. In this instance the free soap forming acid, e. g. abietic(rosin), oleic, stearic, palmitic, etc., is added first to the reclaimedrubber, either on the mill or in the internal mixer, and followed laterin the mixer by the equivalent amount or dry ground caustic soda orpotash after 4-15% water has been worked into-the pulling mass. Theosmotic pressure oi. the natural latex and the dispersion of reclaimedrubber may be measured in various ways as known to those skilled in theart, the measurements 01 relative osmotic pressure in the examplestabulated below, however, being made by the method of R. S. Lillie, Am.J. PhysioL, vol. 20, p. 127, 1907-08. The osmotic pressures of theaqueous soap dispersions of reclaimed rubber are dependent on variousfactors, such as the type of reclaim, the kind of soap used as thehydrophilic colloid for dispersing the rubber, and the concentration ofthe rubber and soap in the dispersion of reclaimed rubber.

In the following table the various aqueous soap dispersions. of reclaimwere mixed with a natural latex of 38% solids and having a relativeosmotic pressure of 34 cm. by the method of Lillie above referred to.The tables show various aqueous soap dispersions of reclaimed rubber,the relative osmotic pressure of the same, and the condition on mixingwith the natural latex having a relative osmotic pressure of 34 cm. -Thefirst table gives various examples of whole tire reclaim, and the secondtable shows data relatingto various tube reclaim.

Table 1 Condition on mixing h fg fi g g g Osmotic presreclaimed rubberdisclaim, kind of soap c1 suredoi rgi) PBtI'SlOII: wiith nzitltiiral ameru er aeravngi'ea ve g coneenmflon of dispersion osmotic pressure ofCubic meters 1. Whole tire (NaOH) re- Ooagulated at once.

claim on 4% K rosinate50% solids.

2. Whole tire (NaOH) re-' 34 No coagulation or gelclaim on 4 a K '05-lation alter two mate-28 solids months.

(same as 1 supra diluted to 28% solids).

3. Whole tire (KOH) re- 78 Coagulated almostim claim on 4% Krosmediately. mate-50% solids.

4. Whole tire (NaOH) re- 45 Gelledaiter 3-4 days- 0181111 on Coaguiatedin less oleate50% solids. than one month.

5. Whole tire (KOH) re- 34 No coagulation or gelclaim on a K lationafter one chaste-50% solids. month.

6. Whole tire (N aOH) re- 80 Cosgulated at once.

aim on 4% Na rosinste-50% solids.

7. Whole tire (NaOH) re- 47 Gellation started after claim on 4% Na onemonth. donate-50% solids.

Table 2 Condition on mixin 313mm 0! Osmotic presreclnimed rubber dismbbe' sure of rersion with natural claim d claimed rubber to: havingrelative and mama on of dispersion osmotic pressure of solids 34 cm.

.Cttbic meter:

1. Tube (N aOH) reclaim 45 Coagulated within one on 6% K rosinatehour.60%solids. Y

2. Tube (KOH) reclaim 43 Coagulated within one on 6% K rosinatehour.

50% solids.

3. Tube (NaOH) reclaim 35 No coagulation or gelon 6% K chaste-50% latlonalter two solids. months.

4. Tube (KOH) reclaim 32 No coagulation or gelon 6% K oleate50% tionafter two so 5. months.

5. Tube (NaOH) reclaim 33 N0 coagulation or gelon 6% Na oleatelationafter one 50% solids. month. I

6. Tube (NaOH) reclaim 45 Coagulation within on 6% N a roeinatethirtyminutes.

50% soil It will be seen from the above results that the mixing withnatural latex of an isotonic aqueous soap dispersion ofreclaimed rubberproduces a mixture stable over an extended period of time. Convenientmethods for adjusting the osmotic pressure of an artificial aqueousdispersion of rubber to agree with a natural latex so as to becomeisotonic with the same are (1) determination of percent colloid requiredin any reclaimed rubber dispersion to give the desired osmotic pressureat a definite solids concentration, and (2) dilution of the artificialdispersion until osmotic pressure agrees with that of the natural rubberlatex. The second method is well illustrated in Table 1 above withrespect to Examples 1 and 2. As shown there, a rosin soap dispersion ofwhole tire reclaim of-50% solids content (Example 1) with a relativeosmotic pressure of 60 cm. when admixed with a natural latex having arelative osmotic pressure of 34 cm. coagulated at once. This samedispersion was diluted with water to 28% solids content to produce adispersion with a relative osmotic pressure of 34, (Example 2), and amixture of this diluted dispersion with the latex was stable and showedno tendency to coagulate after two mouths. On the other hand if theosmotic pressure of the dispersion is too low, e. g. less than 34 cm.,then additional soap may be added to raise osmotic pressure to thedesired level.

From the above tables, it is seen that natural rubber latex may beadmixed satisfactorily with an aqueous soap dispersion of reclaimedrubber. having approximately the some osmotic pressure as the naturallatex. So long as the aqueous soap dispersion of reclaimed rubber hasapproximately the same osmotic pressure as originally present in thenatural latex, the natural latex may have its osmotic pressureartificially changed, as for example by the addition of soap prior toadmixture with the dispersion of reclaim without efiecting the stabilityof the final system adversely. It is only necessary that the naturallatex before any such treatment have approximately the same osmoticpressure as the dispersion of reclaim which is to be mixed therewith. Itis not entirely satisfactory, however, to adjust a natural latex to ahigher osmotic pressure than normal, as by the addition of soap, inorder to have the osmotic pressure of the treated latex equal theosmotic pressure of an artificial dispersion of the reclaim beforeadmixing. Similarly, a processed latex, where certain of the serumsolids have been removed, will not give entirely satisfactory results,

even ii the relative osmotic pressures of such a processed latex and thedispersion of reclaimed rubber are equal at the time of mixing. In thelatter cases, it has been found more satisfactory to restrict anyadjustment of osmotic pressure to the artificial aqueous dispersionrather than to the natural aqueous dispersion. Furthermore, forpractical purposes it is desirable to adjust the osmotic pressure of thereclaim dispersion to that originally occurring in the natural latexprior to any "processing which might modify the serum solids, etc.rather than to any final osmotic pressure of the latex system afterprocessing. In other words it is more important that the osmoticpressure of the reclaim dispersion be in agreement with and based on theosmotic pressure of the natural rubber latex as it normally occursrather than with or on any later osmotic pressure resulting fromprocessing such latex. Once the osmotic pressure of the reclaimdispersion is in agreement with the initial osmotic pressure of thenatural latex it appears that no further adjustment is required and thelatex may be added at once or after processing steps without reducingthe stability of final mixture. The order of mixing, that is adding thelatex to the dispersion or vice versa, appears to make no differenceprovided that the dispersion of reclaimed rubber has approximately thesame osmotic pressure as the natural latex with which it is mixed.

While specific embodiments of the invention have been described, it isobvious that numerous modifications may be made therein and it is notdesired to limit the invention otherwise than as set forth in theappended claims.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:

l. The method of making a stable composition containing natural rubberlatex and an aqueous soap dispersion of reclaimed rubber comprisingpreparing an aqueous soap dispersion of alkali reclaimed rubber havingapproximately the same osmotic pressure as the natural latex and mixingthe said dispersions.

2. A stable composition comprising natural rubber latex and an aqueoussoap dispersion of alkali reclaimed rubber having approximately the sameosmotic pressure as the natural latex.

3. The method of preparing a stable mixture containing natural rubberlatex and an aqueous dispersion of reclaimed rubber comprising mixingwith natural latex an isotonic aqueous soap dispersion of alkalireclaimed rubber.

4. A stable composition comprising natural rubber latex and an isotonicaqueous soap dispersion of alkali reclaimed rubber.

5. The method of preparing a stable mixture containing natural rubberlatex and an aqueous dispersion of alkali reclaimed rubber comprisingmixing with natural latex a reclaimed rubber dispersion which has beendispersed on the amount and type of soap forming constituents necessaryto provide an artificial aqueous dispersion at any desired total solidscontent isotonic with the natural rubber latex.

6. The method of preparing a stable mixture containing natural rubberlatex and an aqueous dispersion of alkali reclaimed rubber comprisingmixing with natural latex an aqueous soap dispersionof reclaimed rubberwhich has been diluted to a total solids content necessary to providethe same osmotic pressure as normally occurring in the natural rubberlatex.

ARTHUR E. BARNARD. WILLIAM E. li/iESSER.

CERTIFICATE or CORRECTION. 3

Patent No.' 2,044,046. June 16, 1936.

ARTHUR E. BARNARD. ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,second column, line 38, in the table, center column, for "Cubic meters"read Centimeters;- page 2, first column, line 8, in the table, centercolumn, for "Cubic meters" read centimeters; and that the said LettersPatent should be read with these corrections therein that the same mayconform to the record of the case in the Patent Office.

Signed and sealed this 8th day of September, A. D. 1956.

Leslie Frazer (Seal) Acting Commissioner of Patents.

